code: def check_backward(
      self, x_data, t_data, w_data, samples_data, gy_data
  ):
      def _black_out(x, t, W, samples):
          return functions.black_out(x, t, W, samples, self.reduce)
  
      gradient_check.check_backward(
          _black_out,
          (x_data, t_data, w_data, samples_data),
          gy_data,
          dtype="d",
          atol=1e-2,
      )
  
file_path: chainer/tests/chainer_tests/functions_tests/loss_tests/test_black_out.py
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
label_desc: Use image node_id 5 for calling the TestBlackOut obj's underlying member method code with example usage: obj.check_backward(x_data, t_data, w_data, samples_data, gy_data) and returns: functions